1. Field of the Invention
The present invention relates to injectors for burners which have a longitudinal axis and applies in particular to methods for producing clinker, which is an intermediate in the manufacture of cement.
2. Description of the Related Art
Clinker is obtained by firing quarry materials such as clay, limestone, etc. at high temperature.
A distinction is made between three main types of firing for producing clinker, namely firing using the wet process, firing using the semi dry process and firing using the dry process.
In the case of the semi dry and dry processes, the firing installation comprises, in succession, a precalcination device for preheating, dehydrating and decarbonating the raw materials, for example a Lepol grate, and a rotary kiln into which the material flows and where it is turned into clinker. This rotary kiln outputs clinker.
A main blast pipe is located at the outlet of the rotary kiln. This blast pipe supplies the rotary kiln with the required calorific energy. The calorific energy needed to operate the precalcination device is provided mainly by the flue gases produced by the main blast pipe, these flue gases circulating in the rotary kiln against the current of the material. Top-up energy is needed at the precalcination device.
In the case of a Lepol grate, this top-up is usually provided by burning, firstly a main fuel with a high lower calorific value (LCV), for example one higher than 6,000 th/t, and secondly, an auxiliary fuel with a low LCV, for example one below 2,000 th/t.
In general, the main fuel consists of liquid industrial waste containing up to 30% by mass of water and the auxiliary fuel consists of contaminated industrial waste water. To provide the top-up energy in the chamber of the precalcination device, pressurized air is used to atomize these fuels in separate injectors.
The oxygen contained in the flue gases present in the chamber of the precalcination device constitutes the main oxidizer. Top-up oxygen is introduced using a third injector near to the main-fuel injector.
In the precalcination device, the main fuel is atomized in the form of an upper layer, the auxiliary fuel is atomized in the form of a lower layer spaced away from the upper layer, and the top-up oxygen is injected in the form of an intermediate layer located between the other two layers, near the upper layer.
The main and auxiliary fuels and the top-up oxidizer do not mix well because they are injected as parallel layers.
As a result, the combustion efficiency of the fuels that are to be injected is relatively low and it is also found that the consumption of the oxygen present in the flue gases is also relatively low.
What is more, the injection system as a whole is bulky.
The object of the invention is to solve these problems by providing improved injectors which, in methods for producing clinker, allow the combustion efficiency of the fuels to be improved and the bulk reduced.
To this end, the subject of the invention is an injector for a burner having a longitudinal axis, characterized in that it comprises an assembly for injecting a main fuel, exhibiting a main-fuel outlet, an assembly for injecting an oxidizer, exhibiting an oxidizer outlet, and an assembly for injecting an auxiliary fuel, exhibiting an auxiliary-fuel outlet, and in that the said assemblies for injecting the main and auxiliary fuels and the oxidizer are arranged radially one around the other.
According to particular embodiments, the injector may have one or more of the following features, taken in isolation or any technically feasible combination:
one or each fuel-injection assembly is an assembly for atomizing the said fuel which comprises means for routing the said fuel, means for routing an atomization fluid, and atomization means connected to the said means for routing the fuel and the atomization fluid;
for the said or each fuel-atomization assembly, the said means for routing the fuel and the atomization fluid are arranged radially around each other;
for the said or each fuel-atomization assembly, the means for routing the atomization fluid are arranged around the means for routing the said fuel;
one or each fuel-injection assembly is mounted in the injector so that it can slide and be adjusted, with respect to the oxidizer-injection assembly, between at least one separated position and one close position, the corresponding fuel outlet and the oxidizer outlet being respectively separated from each other and close together in the said separated and close positions;
the or each fuel-injection assembly is removable;
the oxidizer-injection assembly is arranged radially between the assembly for injecting the main fuel and the assembly for injecting the auxiliary fuel;
the assembly for injecting the fuel with the lower lower calorific value is located radially further towards the outside of the injector than the assembly for injecting the fuel with the higher lower calorific value;
the assembly for injecting the fuel with the lower lower calorific value is located radially on the outside of the injector;
the injector comprises means for causing one or each fuel and/or the oxidizer leaving the corresponding injection assembly to rotate about the longitudinal axis of the injector;
the said rotation-inducing means comprise channels which are in a helical shape with respect to the said longitudinal axis of the injector;
the said channels make an angle of between about 0 and 30xc2x0 with the longitudinal axis of the injector;
the injector comprises an atomization tip which has calibrated orifices and which is mounted downstream of the respective outlets of the assemblies for injecting the main and auxiliary fuels and for injecting the oxidizer; and
calibrated orifices of the atomization tip define between them, in a longitudinal plane of the injector, an angle of between about 20 and 120xc2x0.
Another subject of the invention is a system for injecting main fuel and auxiliary fuel and oxidizer, comprising a source of main fuel, a source of auxiliary fuel, a source of oxidizer, and at least one injector, characterized in that the injector is an injector as described hereinabove and in that the assemblies for injecting the main and auxiliary fuels and the oxidizer of the injector are connected respectively to the sources of main and auxiliary fuel and of oxidizer.
As an alternative, one or each fuel-injection assembly is an assembly for atomizing the said fuel which comprises means for routing the said fuel, means for routing atomization fluid, and atomization means connected to the said means for routing the said fuel and the atomization fluid, and the injection system further comprises at least one source of atomization fluid connected to the said means for routing the atomization fluid of the or each fuel-atomization assembly.
Furthermore, the source of oxidizer may be a source of gas containing between 30 and 100% oxygen.